The present invention relates to a lens and a lens holding device, and more particularly, to a lens provided with a connector on its joint surface and a lens holding device for securing a lens or lenses to a lens barrel.
Compound lenes in which two or more separate pieces of single lenses are cemented together are well known. FIG. 1 illustrates an example of a conventional lens of this type. Specifically, the compound lens is constructed in such a manner that a lens 1 which has a convex surface 1a of a radius of curvature of r.sub.1 and a concave surface 1b of a radius of curvature of r.sub.2, as shown in FIG. 2A, and another lens 2 which has a convex surface 2a of a radius of curvature r.sub.3 (r.sub.2 =r.sub.3) and a convex surface 2b of a radius of curvature of r.sub.4 are cemented together through a cement layer 3 on the concave surface 1b and the convex surface 2a.
There is no problem in conventional lenses of the type when both component lenses 1, 2 to be cemented are made of glass. However, such lens has the following disadvantages when one or both of lenses 1, 2 are made of plastic.
When a glass lens and a plastic lens are cemented, for example, lens 1 being made of glass and lens 2 being made of plastic, through a cement layer 3, the cement layer 3 will shrink as it solidifies with the result that the convex surface 2a may be deformed resulting in a change of its radius of curvature r.sub.3, the occurrence of wrinkles or undulation, or the like. Accordingly, the compound lens may not achieve the expected performance and there is the possibility that it will be unsuitable for use. In addition, even if the deformation resulting from the cementing operation is allowable from the viewpoint of design, other problems may result during use of the lens a compound lens is exposed to a changes in temperature and/or humidity during use with the result that the cement layer 3 may be exfoliated or the convex surface 2a of lens 2 may be deformed to a greater degree (e.g., more than ten times) than when the lens is initially cemented together. This will prevent effective use of the lens during practical application. Also, since the material of lens 2 is plastic, it is acted upon by a cement causing the convex surface 2a to be deformed, causing a failure to achieve the desired function.
Similar disadvantages may also occur when the lens 1 is made of plastic and the lens 2 is made of glass.
When both lenses 1, 2 to be cemented through the cement layer 3 are made of plastic, the concave surface 1b and the convex surface 2a is acted upon by the cement, with the resulting that the function as the lens may not be fulfilled. Even when a cementing agent which does not act upon the plastic material of the lenses 1, 2 is used, the lenses are subject to a change in their configurations (mainly the radius of curvature) during the cementing operation. since both lenses 1, 2 should be cemented applying a pressure force in the direction of the optical axis. At this time, the cement layer 3 solidifies in this deformed state with the result that it is difficult to maintain the designed radii of curvature of the lenses. Furthermore, if the cement layer 3 does not solidify uniformly, large astigmatism will be created in the compound lens and this is a big problem in aberration of a lens. In addition, as in the case where lenses of glass and plastic are cemented, when the compound lens made entirely of plastic is subject to a change of temperature and/or humidity during practical use, exfoliation or a change in configuration of the lens is created and thus it is difficult to maintain expected performance of the lens.
There has also been widely used a lens holding device employing a retainer ring for fitting a lens within a lens barrel. In FIG. 3, which illustrates an example of a conventional lens holding device, a lens fitting portion 4a in the shape of a ring abuts the inner cylindrical wall of a lens barrel 4 and a female screw threads 4b are provided on the inner wall surface rearwardly of the lens fitting portion 4a (the right side in FIG. 3, the same applies to the following description) so that a retainer ring 6 which has male threads 6a on the outer circumferential surface can be detachably engaged with the female screw threads 4b. In this lens holding device, a lens 5 is inserted into the lens barrel 4 and after the outer periphery 5a of lens 5 abuts against a shoulder surface 4c of the lens fitting portion 4a, the retainer ring 6 is threaded into the barrel 4. Subsequently, the lens 5 is restrained against the shoulder surface 4c by the retainer ring 6 and thus is fixed within the barrel 4.
However, in the conventional lens holding device employing the retainer ring 6, the lens 5 is fixed by the tightening force of the retainer ring 6 so that distortion may be caused in the lens 5 or the holding effect of the lens 5 becomes unreliable due to a change in the lens 5 with the lapse of time. In addition, when the lens 5 is made of plastic, the lens 5 may be damaged by the retainer ring 6 and the lens barrel 4 at its surface abutting thereagainst.